Ready-to-use electroporation cuvette including frozen electrocompetent cells

ABSTRACT

A ready-to-use electroporation cuvette is provided that includes a cuvette, first and second electrodes positioned within the cuvette and electroporation competent cells frozen in a suspension solution within the cuvette, wherein the electroporation cuvette is configured to permit electroporation of the cells when the cells are thawed. The electroporation cuvette may be sealed with a cap that may be color coded to aid the user.

This application claims priority to U.S. Provisional Application No.60/556,380 filed Mar. 26, 2004, the contents of which are incorporatedherein by reference in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention provides an apparatus and methods for thetransformation of cells by electroporation. More particularly, theinvention provides a ready-to-use cuvette for electroporation andmethods Of making and using such a cuvette.

2. Description of the Related Art

Introducing nucleic acids into cells is central to many types ofbiological experiments and biotechnology development methods. Forexample, when searching for a gene of interest in a cDNA library, thelibrary must be transferred into a host organism. Among the variousmethods used for introducing nucleic acids into host cells,electroporation has gained widespread use. Exemplary methods and kitsfor performing electroporation are disclosed in U.S. Pat. Nos. 4,910,140and 5,186,800 to Dower, and U.S. Pat. No. 6,338,965 to Greener et al.,each of which is incorporated herein by reference in their entirety.

In general, electroporation involves the transfer of nucleic acids intoa host cell by exposure of the cell to a high voltage electric impulsein the presence of the nucleic acids, such as genes or gene fragments.Typically, host cells are stored by freezing them at a temperature thatpreserves their viability for a long term. The frozen cells are storedin a separate container and must be defrosted, mixed with nucleic acidand subsequently transferred to a cuvette prior to electroporation.

An example of an electroporation method is disclosed in U.S. Pat. No.5,186,800 and involves growing bacteria in enriched media (of any sort)and concentrating the bacteria by washing in a buffer containing 10%glycerol. DNA is added to the cells, the DNA and cells are mixed and theresulting mixture is subjected to an electrical discharge (pulse), whichtemporarily disrupts the outer cell wall of the bacterial cells andpermits the DNA to enter the cells.

The efficiency of nucleic acid transfer depends on a variety of factors,including the electrical field strength, the pulse decay time, the pulseshape, the temperature in which the electroporation is conducted, thetype of cell, the type of suspension buffer, and the concentration andsize of the nucleic acid to be transferred. Researchers have modifiedthe host cell suspension materials to aid in freezing the cells beforethe electrical treatment. Methods disclosed in U.S. Pat. No. 6,338,965include the addition of sugars or sugar derivatives, e.g., sugaralcohols, to host cells suspended in a substantially non-ionic solution,either prior to initial freezing, or after thawing, but prior toelectrotransformation, which improve electroporation efficiency.

Known methods of preparing frozen cells for electroporation requirethawing the cells and mixing with nucleic acid prior to adding them to asuitable electroporation cuvette. This sequence of steps has always beendeemed essential for at least two reasons: first, the structures of anelectroporation cuvette are precisely dimensioned in order to providereproducible electrical field strengths in the cell solution, and thefreezing procedures necessary to store cells in the cuvette wereconsidered too harsh to maintain these precise dimensions; second, thesize of the cuvette chamber was considered too small to allow efficientmixing of cells with nucleic acid. Efficient mixing of cells and nucleicacid is essential to achieving a desired level of cell transformation byelectroporation. The steps of thawing and mixing host cells prior toelectroporation require experimenter's time and presents an opportunityfor contamination or experimental errors that may impact results ordiminish electrotransformation yields. Accordingly, there is a need fora method and equipment that will eliminate the need to separately thawand prepare cells before placing them in an electroporation cuvette.

SUMMARY OF THE INVENTION

According to an embodiment of the present invention, an electroporationcuvette includes a cuvette, first and second electrodes positionedwithin the cuvette, and cells in a suspension solution frozen within thecuvette, wherein the electroporation cuvette is configured to permitelectroporation of the cells when the cells are thawed.

According to another embodiment of the present invention, a method ofmaking a ready-to-use electroporation cuvette includes fabricating anelectroporation cuvette comprising a cuvette, and first and secondelectrodes positioned within the cuvette, sterilizing theelectroporation cuvette, placing an aliquot of electrocompetent cells inthe electroporation cuvette, placing a sterile cap on theelectroporation cuvette, and freezing the aliquot of electrocompetentcells within the electroporation cuvette, such as flash freezing, suchas by dipping the cuvette in liquid nitrogen. The method may alsoinclude sealing the electroporation cuvette in a sterile package.

According to another embodiment of the present invention, a method ofusing a ready-to-use electroporation cuvette includes thawing cellswithin the electroporation cuvette, adding nucleic acid to the cells,placing the electroporation cuvette in an electroporation machine andconducting electroporation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of an exemplary ready-to-use electroporation cuvetteaccording to an embodiment of the present invention.

FIG. 2A is a plane view of an exemplary electrode suitable for use in aready-to-use electroporation cuvette according to an embodiment of thepresent invention. FIG. 2 b is a cross-sectional diagram of theelectrode illustrated in FIG. 2A.

FIG. 3 is a diagram of a ready-to-use electroporation cuvette accordingto another embodiment of the present invention.

FIG. 4 is a plane view of a ready-to-use electroporation cuvetteaccording to another embodiment of the present invention.

FIG. 5 is a process flow diagram for making an electroporation cuvetteaccording to an embodiment of the present invention.

FIG. 6 is a process flow diagram for using an electroporation cuvetteaccording to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

Surprisingly it has been found that host cells, such as electrocompetenthost cells, may be frozen in a suitable electroporation container, suchas an electroporation cuvette according to the present invention, andthen thawed, mixed with nucleic acid, and efficiently transformed byelectroporation directly in the same container. This result is highlysurprising because the conventional wisdom has been that containers suchas electroporation cuvettes cannot withstand the rigors of the freezingprocedures necessary to store competent cells, the relatively large massof the cuvette would interfere with the rapid freezing of the cellsuspension believed to be crucial to the long-term viability of thecells, and that the containers are too small to allow adequate mixing ofthe cells with nucleic acid after thawing. This surprising discoverypermits the preparation and distribution of “ready to use”electroporation containers, such as cuvettes, that contain host cellssuitable for electroporation and that permit rapid “one pot”transformation of the cells with a desired nucleic acid source.

Reference will now be made in detail to exemplary embodiments of thepresent invention. Wherever possible, the same reference numbers will beused throughout the drawings to refer to the same or like parts.

Referring to FIG. 1, according to an embodiment of the presentinvention, a ready-to-use electroporation cuvette 1 includes a vessel 2,referred to herein as a cuvette 2, containing first and secondelectrodes 3, 4 between which is a volume 5 in which an aliquot of cellsin a suspension solution 6 are deposited and maintained in the frozenstate until ready for use. The electroporation cuvette may also includea cap 7 which can be securely attached to the top of the cuvette 2.

The means for attaching the cap 7 to the cuvette 2 may be chosen from anumber of structures that permit a fluid-tight and/or biologically-proofbarrier, such as with a plastic deformation fit, compression fit, screwor bayonet fitting, detent structure 8 and groove fit, gasket andsealing surface fit, or similar removable closure mechanism.Alternatively or additionally, the cap may be sealed to the cuvette suchas by an adhesive, shrink-wrap plastic, or glass that may be broken toremove the cap in preparation for using the cuvette.

The cuvette 2 is preferably made of a material suitable for exposure tocold temperatures, such as for example liquid nitrogen temperatures(about 77K, −196° C.), and very high voltages or electric fieldstrengths. The cuvette material is selected to be compatible both withrapid codling rates, such as may be experienced when the cuvette 2 isdipped into a low temperature bath (such as that used for “flashfreezing” cells, for example, a liquid nitrogen bath, or a dryice/ethanol bath), and with high voltage fields generated in theelectroporation process. It is also preferable that the cuvette materialbe transparent. In an embodiment, the cuvette is made from apolycarbonate material, for example the polycarbonate materialconventionally used for commercially available cuvettes, such as thoseavailable from, for example, Bio-Rad Laboratories (Hercules, Calif.).The cuvette 2 may be manufactured by injection molding or similarmechanism that produces a seamless structure With dimensional controlover internal and external surfaces.

The electrodes 3, 4 are made of a conductive) material, preferably ametal and more preferably aluminum. In an embodiment, the electrodes 3,4 are plates that are positioned to be parallel to each other and at afixed distance apart. In an embodiment, the internal structure of thecuvette includes structure, such as ledges or walls, that hold theelectrode plates in a precise position, parallel to each other and at afixed distance apart from top to bottom. In an alternative embodiment,the electrodes are formed so as to be self-positioning in the cuvette,such as with a wall structure 9 that can be placed against or glued to awall of the cuvette 2, to hold the electrode surface at a preciseposition.

In an embodiment, electrodes 3, 4 are fabricated to be smooth in orderto deliver a consistent electrical field across the entire surface, andtherefore a uniform electric current through the cells. Such electrodesmay be formed from aluminum plates by cleaning and then etching thesurfaces to remove raised points and contaminants, rendering theelectrodes smooth.

The electrodes 3, 4 may be separated by a dimension that is set toprovide a predetermined electrical field through the suspension solutionand cells 6 that is determined to result in a high yield ofelectroporation transformation of the cells. For example, cuvettescontaining bacteria, such as E. coli, may have electrodes 3, 4 separatedby about 0.1 cm to about 0.2 cm. In another example, cuvettes containingyeast may have electrodes 3, 4 separated by about 0.2 cm. In yet anotherexample, cuvettes containing mammalian cells may have electrodes 3, 4separated by about 0.4 cm.

In an embodiment, the electrodes 3 are in the form of an “I” beam asillustrated in FIGS. 2A and 2B. In this embodiment, an electrode 3comprises a first plate 20 and a second plate 22 connected by aperpendicular interconnecting plate 23 or plates to form the “I” beamshape. As illustrated in the cross-sectional view of FIG. 2B, theinterconnecting plate 23 positions the first and second plates 20, 22 afixed distance apart. The interconnecting plate 23 also maintains thefirst plate 20 parallel to the second plate 22. The distance separatingplates 20, 22, which forms a gap 24, is determined by the span ofinterconnecting plate 23. This configuration has advantages infabrication because either the first or second plates (20 or 22) maycontact the cell suspension fluid to function as the electrode surface,permitting the other surface to contact and/or be attached to a wall ofthe cuvette 2. If the cuvette 2 has a rectangular or square crosssection, then the position and orientation of the electrode 3 in thecuvette 2 is determined by the electrode itself, in particular by theinterconnecting plate 23. In this manner, a standard size cuvette (e.g.,one with a square cross-section) may be used to provide electroporationcuvettes with different distances between the electrodes by using “I”beam electrodes having different spans of interconnecting plate 23.Further, the “I” beam electrodes have sufficient structural rigidity toretain their shape, and thus the controlled distance between respectiveelectrodes, during the freezing and thawing processes.

Returning to FIG. 1, the cap 7 may be made by injection molding of asimilar or different material as the cuvette. In a preferred embodimentthe cap may be color coded or otherwise marked to indicate the type ofcells contained in the cuvette and/or the dimension separating theelectrodes 3, 4, since such information is useful to users of theready-to-use cuvette. The color coding permits the user to easily selectthe proper cuvette for a particular experiment by observing the cap,which is advantageous when a number of cuvettes are stored together in afreezer.

Alternative configurations of the cuvette are contemplated. FIG. 3illustrates an alternative embodiment featuring structures to permitpositioning within an electroporation machine. For example, the cuvette1 may include a seating ledge 30 that may interface with a complementarystructure on the electroporation machine. Also, the cuvette 1 mayinclude a handling structure or flange 31 to permit easy handling of thecuvette 1 without conducting heat into the cells or riskingcontamination of the interior. The cuvette 1 may also include electricalconnections 32, 33 for ease of connecting the electrodes (not shown inFIG. 3) to the electroporation machine.

In another alternative embodiment illustrated in FIG. 4, theelectroporation cuvette 1 may be formed by fusing the cuvette 2 with “I”beam electrodes 3. In this embodiment, two walls 41 of the cuvette 2pass through the gap 24 (see FIG. 2B) in the “I” beam so that one of theelectrode plates 20 forms a portion of the exterior to the cuvette 2,permitting that plate 20 to serve as an electrical contact surface 40for interfacing electrically with the electroporation machine. On theinside, the other electrode plate 22 forms a portion of the interior ofthe cuvette 2, where it functions as the electrode surface 44. In thisembodiment, the interconnecting plate 23 (FIG. 2B) conducts electricitybetween the exterior facing plate 20 and the interior face plate 22. Theexterior surface of the cuvette 2 may also feature position-orientingstructures, such as a tab 45, that interfaces with a correspondingstructure in the electroporation machine to ensure the cuvette isinserted in a proper orientation. The cuvette 2 may also featurestructures to strengthen the assembly and to facilitate flow of liquidsinto the gap 46 between electrode surfaces 44, such as a wedge-shapedblend 47. between the upper wall 48 of the cuvette 2 and the electrodesurface 44. As described above with respect to FIG. 2A, 2B, the size ofthe gap 46 in the cuvette 2 may be varied by changing the span of theinterconnecting plate 23 (FIG. 2B), varying the gap 24 between plates20, 21 of each electrode, without varying the outside dimensions of thecuvette 2.

Manufacture and assembly of the ready-to-use cuvette is summarized inFIG. 5. The cuvette is fabricated by a suitable method, such asinjection molding, and electrodes are positioned in the cuvette, whichmay be accomplished by fusing the electrodes into the cuvette, or gluingor force-fitting the electrodes into electrode positioning structure.Step 50. The cuvette may thus be designed and manufactured for a singleuse. An example of a suitable cuvette is the Gene Pulser® Cuvette,Catalog No. 165-2089 manufactured by Bio-Rad Laboratories of Hercules,Calif.

Once assembled, the cuvette is sterilized, step 51. Sterilization mayinclude one or more of chemical cleaning, heat treatment and exposure togamma or X-ray radiation, or other suitable sterilization process.

The cuvette may then be prechilled, such as by suspending it in a waterice bath, in preparation for depositing cells into the cuvette. Step 54.

Cells for electroporation are added to a suitable suspension solution,and then an aliquot of cells and solution are added to the chilledcuvette. Step 54. The cells may be any cells suitable forelectroporation, including for example, bacteria such as E. coli, yeast,plant or mammalian cells. The cells may be treated to render themcompetent for electroporation, which may include using a suspensionsolution that renders the cells electroporation competent. Suitablesuspension solutions are well known in the art.

Once cells and suspension solution have been added, the cuvette issealed with a cap providing a sterile barrier to prevent contamination.Step 54. Cells and suspension solution are then rapidly frozen, such asby flash freezing, step 55, dipping or submerging the cuvette in liquidnitrogen, step 56, dipping or submerging the cuvette in a bath ofethanol and dry ice, step 57, or placing the cuvette in a freezer, suchas a freezer at about −85° C. or a rate-controlled freezer. In variousembodiments of the present invention, the cap may be attached to: thecuvette before or after freezing.

Once the cells and suspension solution have been frozen, the cuvette isstored in a freezer or other suitable cold storage means until ready foruse. Step 58. By maintaining the cuvette below 0° C., such as inultra-cold storage at about −78° C., the cells may be maintained readyfor use for an extended period of time.

Use of the ready-to-use cuvette is illustrated in FIG. 6. Once theappropriate cuvette is selected, such as based upon the color code onthe cap, the cells and suspension solution are gently thawed, such as byplacing the cuvette on wet ice. Step 60. Once thawed, the cap isremoved, step 61, and a suitable amount of a nucleic acid, such as in asuspension solution, is added by a user. Step 62. The nucleic acid ismixed with the cells and suspension solution. Step 63. A suitable methodof mixing nucleic acid and cells/suspension solution within theelectroporation cuvette comprises alternately drawing solution up into amicropipette and expelling the solution down into the cuvette a numberof times, such as 3 or 4 times, followed by rapping the cuvette on asolid surface, such as a laboratory bench.

Once the nucleic acid and cells/suspension have been mixed, the cuvettemay be placed in a suitable electroporation machine, step 64, andelectroporation conducted, step 65. Electroporation machines and methodsfor using them to conduct, electroporation transformation of cells arewell known in the art.

Following electroporation, the cells are placed on or in an appropriatemedium to promote growth of the transformed cells. The chosen mediumshould propagate the transformed cells that either transiently expressor have nucleic acids integrated into the host cells' genome. Further,the medium advantageously should be selected so as to assist the cellsin recovering from the electrical treatment.

Suitable cell suspension solutions are substantially non-ionic solutionsin order to ensure a predictable electric current is produced in thecells. An appropriate non-ionic solution may be a buffer solution withminimal or no ions present. Non-ionic solutions may also be non-polar.The concentration of ions in the buffer is adequately low so that whenelectricity is discharged into the host cells, little or no additionalcurrent is carried into the cells. The presence of ions in the buffermay result in additional current being carried into the cells and canlower the survival rate of the host cells. In some embodiments of theinvention, the non-ionic solution includes glycerol at about 5% to about10% solution or dimethyl sulfoxide from about 2% to about 15% solution,depending upon the application.

The solution may also comprise at least one sugar or sugar derivative,such as D-stereoisomeric or the L-forms (enantiomers) form. Theconcentration of the sugar or derivative may be about 2.0% to about2.5%. In specific embodiments, the added sugar derivative is sorbitoland its concentration is about 2.5%. Specific sugars may include, butare not limited to: aldoses, such as monosaccharides which includetrioses (i.e. glyceraldehyde), tetroses (i.e. erythrose, threose),pentoses (i.e. arabinose, xylose, ribose, lyxose), hexoses (i.e.glucose, marinose, galactose, idose, gulose, altrose, allose, talose),heptoses (i.e. sedoheptulose), octoses (i.e. glycero-D-manno-octulose),pentose ring sugars (i.e. ribofurandse, ribopyranose); disaccharides(i.e., sucrose, lactose, trehalose, maltose, cellobiose, gentiobiose);and trisaccharides (i.e., raffinose), oligosaccharides (i.e., amylose,amylopectin, glycogen).

Sugar derivatives that may be used include, but are not limited to:alditols or aldose alcohol, which include erythritol, glucitol,sorbitol, or mannitol; ketoses, e.g., dihydroxyacetone, erythrulose,ribulose, xylulose, psicose, fructose, sorbose, and tagatose;aminosugars such as glucosamine, galactosamine, N-acetylglucosamine,N-acetylgalactosamine, muramic acid, N-acetyl muramic acid, andN-acetylneuraminic acid (sialic acid); glycosides, such as glucopyranoseand methyl-glucopyranose; and lactones, such as gluconolactone.

Nucleic acids that may be added to the ready-to-use electroporationcuvette may include, but are not limited to, RNA, DNA, or non-naturallyoccurring nucleic acid sequences that encode functional ornon-functional proteins, and fragments of those sequences,polynucleotides, or oligonucleotides. The nucleic acids of interest maybe obtained naturally or synthetically, e.g., using PCR or mutagenesis.Further, the nucleic acids may be circular, linear, or supercoiled intheir topology. Preferably, the nucleic acids may range from about 3 kbto about 300 kb.

i 1

EXAMPLES

Preparation of Ready-To-Use Electroporation Cuvettes. A recA-minusderivative of E. coli strain MC1061 was inoculated into 1 liter of SOB(minus magnesium) growth medium and incubated at 37° C. and 275 rpmovernight (approximately 15 hours). The overnight culture was diluted1:50 into 1.5 liters of SOB (minus magnesium) and grown at 39° C., 275rpm until an OD550 of 1.0 was reached. Cells were harvested bycentrifugation and then washed by resuspending in an equal (to theoriginal) volume of cold (approx. 4° C.) 10% glycerol. The washing stepwas repeated one time. The final cell pellet was resuspended in aminimal amount of 10% glycerol. The final concentration of the cells wasadjusted to ˜250 OD550 units/ml with cold 10% glycerol. The cellsuspension was dispensed in 20 μl aliquots into pre-chilledelectroporation cuvettes (Gene Pulser® Cuvette from Bio-RadLaboratories), flash-frozen by partial immersion of the cuvettes inliquid nitrogen, and then stored in an ultra-cold freezer at about −75°C.

Use of Ready-To-Use Electroporation Cuvettes in Transformation: Thecuvettes prepared according to the procedure described above wereremoved from the freezer and placed on ice for about 10 minutes to thawthe cells. One microliter of pUC19 (10 pg) nucleic acid was pipetteddirectly into the thawed cells and the material was mixed with the cellsin the cuvette by pipetting the combined solution up and down severaltimes. Further mixing of the material was achieved by rapping thecuvette sharply on the bench top several times. The mixture was thensubjected to electroshock using a Bio-Rad Micropulser from Bio-RadLaboratories on pre-programmed setting of “Ec1”. Immediately afterpulsing, the cells were removed from the cuvette by rinsing out theelectrode gap with 980 μl of SOC, and transferring the resulting liquidto sterile snap-cap polypropylene tubes (Falcon 2059). The tubes wereshaken at 275 rpm, 37° C. for about 1 hour. The liquid was then diluted1:100, and 100 μl of this dilution was plated onto LB+100 μg/mlampicillin plates and incubated overnight at 37° C.

The foregoing description of various embodiments of the invention hasbeen presented for purposes of illustration and description. It is notintended to be exhaustive or to limit the invention to the precise formdisclosed, and modifications and variations are possible in light of theabove teachings or may be acquired from practice of the invention, theembodiments were chosen and described in order to explain the principlesof the invention and its practical application to enable one skilled inthe art to utilize the invention in various embodiments and with variousmodifications as are suited to the particular use contemplated.

1-43. (canceled)
 44. An electroporation cuvette with an internalstructure comprising: first and second electrodes positioned at a firstfixed distance apart within the electroporation cuvette, wherein each offirst and second electrodes is in the form of an I-beam, each I-beamcomprising (i) inner, and (ii) outer plates that are connected by atleast one perpendicular interconnecting plate, the length of whichdetermines, between the inner and outer plates, a second fixed distance;a first space formed between the first and second electrodes; whereinthe length of at least one of the interconnecting plates of the firstand second electrodes may be varied to enable a change in the firstfixed distance between the first and second electrodes.
 45. Theelectroporation cuvette of claim 44 wherein the first and secondelectrodes positioned within the electroporation cuvette are held inposition by ledges or walls within the electroporation cuvette.
 46. Theelectroporation cuvette of claim 44 wherein at least one of the firstand second electrodes is placed against and fixed to one of the insidewalls of the electroporation cuvette.
 47. The electroporation cuvette ofclaim 44 wherein the first and second electrodes are positioned parallelto each other.
 48. The electroporation cuvette of claim 45 wherein thefirst and second electrodes are positioned parallel to each other. 49.The electroporation cuvette of claim 46 wherein the first and secondelectrodes are positioned parallel to each other.
 50. Theelectroporation cuvette of claim 44 further comprising a second spaceformed in the upper portion of the electroporation cuvette above thefirst space, wherein the structure defining the boundaries of the secondspace comprises a wedge-shaped blend between the upper walls of theelectroporation cuvette and the first and second electrodes, wherein thewedge-shaped blend provides a transition from the second space into thefirst space to facilitate the flow of liquids into the first space. 51.The electroporation cuvette of claim 50 wherein the structure definingthe boundaries of the second space comprises one or more ledges to holdfirst and second electrodes in a fixed position during electroporation.52. The electroporation cuvette of claim 44 wherein at least one of thefirst and second electrodes is placed against a one of the lowerinside-walls of the electroporation cuvette.
 53. The electroporationcuvette of claim 52, wherein the first and second electrodes arepositioned parallel to each other.
 54. The electroporation cuvette ofclaim 44 wherein the inner and outer plates of the I-beam electrodeshave sufficient structural rigidity to retain their shape, meaning thatthe fixed distance between the electrodes is maintained during freezingand thawing processes.
 55. The electroporation cuvette of claim 44wherein at least one of the first and second electrodes comprises ametal.
 56. The electroporation cuvette of claim 44 wherein at least oneof the first and second electrodes comprises aluminum.
 57. Theelectroporation cuvette of claim 44 wherein the first electrode is fixedto the inside wall of the cuvette and the second electrode is placedagainst the inside wall opposite the first electrode of the cuvette,wherein the electrodes are positioned at a fixed distance apart.
 58. Theelectroporation cuvette any of claim 50 wherein the structure definingthe boundaries of the second space comprises one or more ledges to holdthe second electrode in a position during electroporation.
 59. Anelectroporation cuvette with a structure comprising; first and secondelectrodes (i) positioned at a fixed distance apart, and (ii) fused totwo of the directly opposing, lower walls of the electroporationcuvette; wherein each of first and second electrodes is in the form ofan I-beam, comprising: parallel (i) inner, and (ii) outer plates thatare connected by at least one perpendicular and variable-lengthinterconnecting plate, the length of which determines a second fixeddistance between the inner and outer plates of each of first and secondelectrodes; wherein the directly opposing, lower walls of theelectroporation cuvette pass through a second fixed distance between theinner and outer plates of each of the first and second electrodes;wherein the outer plate of each of the first and second electrodes formsthe lower exterior, and the inner plate of each of the first and secondelectrodes forms the lower interior, of two of the lower walls of thecuvette-electrode combination; wherein a first space is formed withinthe electroporation cuvette between the inner plates of both the firstand second electrodes; wherein a second space is formed in theelectroporation cuvette, above the first space; wherein the second spaceis continuous with the first space; and wherein the structure definingthe side boundaries of the second space facilitates the flow of liquidsinto the first space.
 60. The electroporation cuvette of claim 59 thevolume of the first space may be varied by varying the length of atleast one of the interconnecting plates of the first and secondelectrodes to alter a second fixed distance between the inner and outerplates of at least one of the first and second electrodes.
 61. Theelectroporation cuvette of claim 59 wherein the parallel inner and outerplates of the I-beam electrodes have sufficient structural rigidity toretain their shape, meaning that the first fixed distance between theelectrodes is maintained during freezing and thawing processes.
 62. Theelectroporation cuvette of claim 59 wherein the inner plate of one ofthe first or second electrodes is configured to function as theelectrode surface; and the outer plate of the other of the first orsecond electrodes is configured to be in contact with one of the lowerinside walls of the cuvette.
 63. An electroporation cuvette with aninternal structure comprising: first and second electrodes positionedwithin the electroporation cuvette and placed against two of thedirectly opposing, lower inside walls of the electroporation cuvette,wherein the first and second electrodes are positioned at a first fixeddistance apart; wherein each of first and second electrodes is in theform of an I-beam, each I-beam comprising (i) inner, and (ii) outerplates that are connected by at least one perpendicular interconnectingplate, the length of which determines the second fixed distance betweenthe inner and outer plates of each of the electrodes; a first spaceformed between the first and second electrodes; and a second spaceformed in the upper portion of the electroporation cuvette, above thefirst-space; wherein the length of at least one of the interconnectingplates of the first and second electrodes may be varied to enable achange in distance between the first and second electrodes, resulting ina change in the volume of the first space; wherein the second space iscontinuous with the first space; and wherein the structure defining theside boundaries of the second space facilitates the flow of liquids intothe first space.
 64. A method of using an electroporation cuvette ofclaim 44 for transformation of a bacteria or yeast cell, comprising:positioning at least one the electrodes inside the cuvette; adjustingand fixing the length of the interconnecting plate; maintaining thefixed length of the interconnecting plate throughout electroporation;wherein the electrode maintains sufficient structural rigidity tocontrol the distance between the electrodes.